A. Technical Field
The present invention relates to a fan blade in particular for smoke venting fans having fastening means for fastening the fan blade to a fan hub and to a blade section.
B. Background of the Invention
Fans for the subway or tunnels and/or closed buildings for vehicles, such as underground garages, must operate reliably under a wide variety of load and ambient conditions for a very long service life. The installation of fans in subways or tunnels or underground garages is typically designed for operation for a period of several years or decades. In particular when using fans as smoke venting fans in subways or tunnels, there are requirements of the operability of the fan at high temperatures, such as those which occur in fires in particular, on the part of the metro operator or tunnel operator. Some of these requirements are set by law. On the other hand, as is customary in general, there is a desire to manufacture the fans in the most favorable possible manner and with savings of materials.
In general, fans in their basic design consist of a fan hub, to which a number of fans blades are attached radially. The fan blades are fastened to the hub by fastening means such as bolts.
Against the background of the general requirements of fans described here, various fan blades are conceivable. To keep the weight low, fan blades may be made of solid aluminum or an aluminum alloy. However, one disadvantage of fan blades made of aluminum is their limited usability at temperatures above approx. 300° C., because the tensile strength of aluminum drops sharply at such temperatures, so that aluminum gradually begins to flow. Even special aluminum alloys are unable to significantly improve upon this unsuitability. As a result of this negative property of aluminum, fan blades may change their shape and/or length at high temperatures, such as those which may occur in fires, for example, thus greatly impairing their use as intended in fires or even making it impossible.
Based on this inadequacy of fan blades made of aluminum, solid fan blades made of steel are used in the state of the art for smoke venting fans exposed to high loads, for example, at high speeds and/or large fan lengths. Fan blades made of steel have the disadvantage, however, of having a very high mass and being expensive to manufacture because of the high use of material.